Rf quadrupole particle accelerator

ABSTRACT

An apparatus may include a drift tube assembly, the drift tube assembly defining a triple gap configuration, and arranged to accelerate and transmit an ion beam along abeam path. The apparatus may include a resonator, to output an RF signal to the drift tube assembly, and an RF quadrupole triplet, connected to the drift tube assembly, and arranged circumferentially around the beam path.

Field of the Disclosure

The disclosure relates generally to ion implantation apparatus and moreparticularly to high energy beamline ion implanters.

Background of the Disclosure

Ion implantation is a process of introducing dopants or impurities intoa substrate via bombardment. Ion implantation systems may comprise anion source and a series of beam-line components. The ion source maycomprise a chamber where ions are generated. The ion source may alsocomprise a power source and an extraction electrode assembly disposednear the chamber. The beam-line components, may include, for example, amass analyzer, a first acceleration or deceleration stage, a collimator,and a second acceleration or deceleration stage. Much like a series ofoptical lenses for manipulating a light beam, the beam-line componentscan filter, focus, and manipulate ions or ion beam having particularspecies, shape, energy, and/or other qualities. The ion beam passesthrough the beam-line components and may be directed toward a substratemounted on a platen or clamp.

Implantation apparatus capable of generating ion energies ofapproximately 1 MeV or greater are often referred to as high energy ionimplanters, or high energy ion implantation systems. One type of highenergy ion implanter is termed linear accelerator, or LINAC, where aseries of electrodes arranged as tubes conduct and accelerate the ionbeam to increasingly higher energy along the succession of tubes, wherethe electrodes receive an powered voltage signal. Known LINACs aredriven by an RF voltage of frequency in the 13.56MHz-120 MHz range.

One issue for operation of RF LINAC ion implanters is that duringacceleration of an ion beam, which ion beam is partitioned into ionbunches along a direction of propagation (Z-direction), a naturaltendency of an ion bunch is to spread out both transversely (inX-direction and Y-direction) as well as longitudinally (in Z-direction,or equivalently, in time). Known methods for focusing ions are generallycomplex and may require unduly lengthy acceleration stages to focus theaccelerating ion bunches.

In some approaches, transverse focusing of ions may be performed addingDC quadrupoles. These DC quadrupoles may be added at various stagesalong a LINAC, which stages include drift tube electrodes that are usedto accelerate the ion bunches. Such DC quadrupoles may be fabricated aselectrostatic or magnetic components that apply a DC quadrupole field toa passing ion beam. The addition of these DC quadrupoles to a LINACinevitably add cost, size and complexity to the beamline and theassociated control systems.

With respect to these and other considerations the present disclosure isprovided.

Brief Summary

In one embodiment, an apparatus is provided. The apparatus may include adrift tube assembly, the drift tube assembly defining a triple gapconfiguration, and arranged to accelerate and transmit an ion beam alongabeam path. The apparatus may include a resonator, to output an RFsignal to the drift tube assembly, and an RF quadrupole triplet,connected to the drift tube assembly, and arranged circumferentiallyaround the beam path.

In another embodiment, an ion implanter may include an ion source, togenerate a continuous ion beam, and a buncher, disposed downstream ofthe ion source, and arranged to transform the continuous ion beam into abunched ion beam. The ion implanter may include a linear accelerator,downstream of the buncher and comprising a plurality of accelerationsstages. A given stage of the plurality of acceleration stages mayinclude a drift tube assembly, the drift tube assembly comprising aplurality of drift tubes, defining a triple gap configuration, andarranged to accelerate the bunched ion beam along a beam path. The givenstage may include a resonator, to output an RF signal to the drift tubeassembly; and an RF quadrupole triplet, connected to the drift tubeassembly, and arranged circumferentially around the beam path.

In a further embodiment, an apparatus may include a drift tube assembly,including a plurality of drift tubes arranged to accelerate and transmitan ion beam along a beam path. The apparatus may include a resonator, tooutput an RF signal to the drift tube assembly, and a quadrupolearrangement, arranged circumferentially around the beam path. Thequadrupole arrangement may be integrated into a surface of the pluralityof drift tubes of the drift tube assembly, and wherein the quadrupolearrangement defines a sinusoidal shape or an elliptical shape.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary apparatus according to embodiments of thedisclosure;

FIG. 2 shows another exemplary apparatus, according to embodiments ofthe disclosure;

FIG. 3 shows a further exemplary apparatus, according to embodiments ofthe disclosure;

FIG. 4 illustrates yet another exemplary apparatus, according toadditional embodiments of the disclosure;

FIG. 5 shows details of the geometry of an apparatus, according toembodiments of the disclosure;

FIG. 6A and FIG. 6B depict the geometry of ion beam focusing inaccordance with embodiments of the disclosure;

FIG. 7A shows another exemplary apparatus, according to furtherembodiments of the disclosure;

FIG. 7B and FIG. 7C present simulation results showing ion beam focusingas a function of gap dimensions is an apparatus arranged according toembodiments of the disclosure; and

FIG. 8 depicts an exemplary ion implanter according to embodiments ofthe disclosure.

The drawings are not necessarily to scale. The drawings are merelyrepresentations, not intended to portray specific parameters of thedisclosure. The drawings are intended to depict exemplary embodiments ofthe disclosure, and therefore are not be considered as limiting inscope. In the drawings, like numbering represents like elements.

DETAILED DESCRIPTION

An apparatus, system and method in accordance with the presentdisclosure will now be described more fully hereinafter with referenceto the accompanying drawings, where embodiments of the system and methodare shown. The system and method may be embodied in many different formsand are not be construed as being limited to the embodiments set forthherein. Instead, these embodiments are provided so this disclosure willbe thorough and complete, and will fully convey the scope of the systemand method to those skilled in the art.

Terms such as “top,” “bottom,” “upper,” “lower,” “vertical,”“horizontal,” “lateral,” and “longitudinal” may be used herein todescribe the relative placement and orientation of these components andtheir constituent parts, with respect to the geometry and orientation ofa component of a semiconductor manufacturing device as appearing in thefigures. The terminology may include the words specifically mentioned,derivatives thereof, and words of similar import.

As used herein, an element or operation recited in the singular andproceeded with the word “a” or “an” are understood as potentiallyincluding plural elements or operations as well. Furthermore, referencesto “one embodiment” of the present disclosure are not intended to beinterpreted as precluding the existence of additional embodiments alsoincorporating the recited features.

Provided herein are approaches for improved high energy ion implantationsystems and components, based upon a beamline architecture, and inparticular, ion implanters based upon linear accelerators. For brevity,an ion implantation system may also be referred to herein as an “ionimplanter.” Various embodiments entail novel approaches that provide thecapability of improved control of an ion beam during accelerationthrough the acceleration stages of a linear accelerator, and inparticular, improved ion beam focusing.

FIG. 1 shows an exemplary apparatus according to embodiments of thedisclosure. The apparatus 100 may represent an acceleration stage of alinear accelerator, such as a linear accelerator arranged within an ionimplanter, as discussed below with respect to FIG. 8. The apparatus 100includes a drift tube assembly 104 and associated components foraccelerating an ion beam in an acceleration stage of a linearaccelerator. In particular, the apparatus 100 defines a triple gapconfiguration, where an ion beam is conducted through three acceleratinggaps within the apparatus 100. As such, the apparatus 100 is arranged totransmit and accelerate a bunched ion beam, shown as an ion beam 130,along a beam path 140, extending along a central region of the apparatus100.

The drift tube assembly 104 is formed of a plurality of drift tubes,including a first grounded drift tube 112, a second grounded drift tube118, a first powered drift tube 114, disposed downstream of the firstgrounded drift tube 112, and a second powered drift tube 116, disposeddownstream of the first powered drift tube 114. The drift tube assembly104 is coupled to a resonator 102, arranged to output an RF signal. Inthe configuration of FIG. 1, opposite ends of the resonator 102 areconnected to the first powered drift tube 114, and the second powereddrift tube 116. Accordingly, when an RF power generator 120 delivers RFpower to the resonator 102, an RF voltage of a first polarity isgenerated on the first powered drift tube 114, while a RF voltage of asecond, opposite, polarity is generated on the second powered drift tube116. The generated RF voltages have sinusoidal temporal variation andhave phase difference of 180 degrees, which variation means the voltageon the first powered drift tube 114 is equal but opposite polarity asthe voltage on the second powered drift tube 116. A sinusoidaltime-varying electric field thus develops across gap 2, proportional totwice the instantaneous value of the RF voltage signal, and varyingaccording to the frequency of the applied RF voltage signal. Likewise,but having different amplitudes time-varying electric fields of the samefrequency develops across gap 1, between the first grounded drift tube112 and first powered drift tube 114, and across the gap 3, between thesecond powered drift tube 116 and second grounded drift tube 118.

Note that the apparatus 100 is arranged to accept the ion beam 130 as abunched ion beam, where the ion beam 130 may be a continuous ion beam,upstream to the apparatus 100, and may be bunched by a buncher (notshown), arranged according to known LINACs. As such, by properlyarranging the timing of the arrival of a bunch of ions of the ion beam130 at the gap 1, gap 2, gap 3, the ion beam may be accelerated byelectric fields that are created when the generated RF voltage on thepowered electrodes reach a maximum value and has the right polarity,i.e., when the voltage drop across the gap is equal to minus theamplitude of the voltage for the gaps, gap1 and gap3 and minus two timesthe voltage amplitude for gap2. In this manner, a given bunch may beaccelerated generally along the Z-axis of the Cartesian coordinatesystem shown. At the same time, the bunched ions may tend to defocus inthe X-direction and Y-direction. To counteract this tendency, theapparatus 100 is equipped with a quadrupole arrangement 108, connectedto the drift tube assembly 104, and arranged circumferentially aroundthe beam path 140.

As shown, the quadrupole arrangement 108 is arranged as a triplet, thetriplet including a first quadrupole 108A, formed on a downstreamportion of the first grounded drift tube 112 and on an upstream portionof the first powered drift tube114. The quadrupole arrangement 108 alsoincludes a second quadrupole 108B, formed on a downstream portion of thefirst powered drift tube 114 and an upstream portion of the secondpowered drift tube 116. The quadrupole arrangement 108 further includesa third quadrupole 108C, formed on a downstream portion of the secondpowered drift tube 116 and on an upstream portion of the second groundeddrift tube 118.

A given quadrupole of the quadrupole arrangement 108 includes two pairsof protrusions, where the protrusions of a given pair are arranged onopposite sides of the beam path 140, and connected to a given drifttube. To define a quadrupole geometry, the protrusions may be arrangedthe following manner: A first line (see line 152) extending throughfirst protrusion pair is rotated 90 degrees about an axis generallydefined by the beam path 140, with respect to a line extending throughthe second protrusion pair (see line 154). While shown as cylinders, theprotrusions may be of any suitable shape according to other embodiments.

Note that the quadrupole arrangement 108 may be formed of conductivematerial that is electrically connected with the drift tube assembly104, so the potential of a given quadrupole component of firstquadrupole 108A, second quadrupole 108B, or third quadrupole 108C ismaintained at the same potential as the potential of drift tube,connected to the given quadrupole component. Thus, the quadrupolearrangement 108 forms an RF quadrupole triplet that generates a timevarying and alternating polarity quadrupole electric field at the samefrequency as the accelerating electrical fields extending along theZ-direction across the gaps- gap 1, gap 2, and gap 3.

In operation, as the ion beam 130 is accelerated through the apparatus100, and an RF voltage signal is applied to the drift tube assembly 104,the quadrupole arrangement 108 will introduce a quadrupole moment intoeach of the gaps, gap 1, gap 2, and gap 3, via first quadrupole 108A,second quadrupole 108B, and third quadrupole 108C. These quadrupoles mayact to produce a classic balanced quadrupole triplet. According to someembodiments of the disclosure, the relative length (along theZ-direction) of the gaps gap 1, gap 2, and gap 3, as well as thequadrupole strength of the gaps may be adjusted independently of oneanother to achieve proper focusing of the ion beam 130. In this manner,the same focusing strength in X and Y directions may be achievedoverall, with similar quadrupole strength fields in alternatingdirections, as indicated by the arrows in FIG. 1. This result may inparticular be achieved by optimizing the size of the protrusions formingthe respective quadrupoles on each side of gapl, gap 2 and gap 3.

Note that in the embodiment of FIG. 1, the cylindrical shapes of theprotrusions forming the respective quadrupoles are not ideal, becausesuch cylinders exhibit sharp corners. These sharp corners may not besuitable for stability in a high field environment, where a relativelyhigher electric field is generated across the gaps, gapl, gap 2, orgap3. Such sharp corners may produce field intensification and serve toinitiate electrostatic breakdown, even in vacuum environments.Accordingly, in additional embodiments, a quadrupole may be formed usingsmoother, more rounded features.

FIG. 2 presents an embodiment showing a drift tube assembly 204 that maybe used as in the case of drift tube assembly 104, to accelerate andshape an ion beam, generally as discussed with respect to FIG. 1. Thedrift tube assembly 204 is formed of a plurality of drift tubes,including a first grounded drift tube 212, a second grounded drift tube218, a first powered drift tube 214, disposed downstream of the firstgrounded drift tube 212, and a second powered drift tube 216, disposeddownstream of the first powered drift tube 214. In this embodiment, aquadrupole arrangement 208 is formed integrally with the drift tubeassembly 204, where the quadrupole arrangement 208 is specificallyformed by shaping portions of the various drift tubes of the drift tubeassembly 204.

More particularly, the quadrupole arrangement 208 is arranged as atriplet, the triplet including a first quadrupole 208A, formed on adownstream portion of the first grounded drift tube 212 and on anupstream portion of the first powered drift tube214. The quadrupolearrangement 208 also includes a second quadrupole 108B, formed on adownstream portion of the first powered drift tube 214 and an upstreamportion of the second powered drift tube 216. The quadrupole arrangement208 further includes a third quadrupole 208C, formed on a downstreamportion of the second powered drift tube 216 and on an upstream portionof the second grounded drift tube 218. Like the quadrupole arrangement108, the quadrupole arrangement 208 may act to focus an ion beam (notshown) in X- and Y-directions, while the ion beam is conducted andaccelerated along the Z-direction through the drift tube assembly 204.

In the embodiment of FIG. 2, the first quadrupole 208A, secondquadrupole 208B, and third quadrupole 208C define a sinusoidal shape, asshown. According to some embodiments, the shapes of the various opposingdrift tubes may form complementary matches to one another. Inparticular, a downstream surface of the first grounded drift tube 212may form a complementary match to an upstream surface of the firstpowered drift tube 214. Likewise, a downstream surface of the firstpowered drift tube 214 may form a complementary match to an upstreamsurface of the second powered drift tube 216, while a downstream surfaceof the second powered drift tube 216 forms a complementary match to anupstream surface of the second grounded drift tube 218. Saiddifferently, the opposing surfaces that form each quadrupole, if broughttogether, may fit one another as a three-dimensional jigsaw coupling.

FIG. 3 presents an apparatus showing a drift tube assembly 304 that maybe used in the manner of the drift tube assembly 104 or drift tubeassembly 204, to accelerate and shape an ion beam, generally asdiscussed with respect to FIG. 1 and FIG. 2. The drift tube assembly 304is formed of a plurality of drift tubes, including a first groundeddrift tube 312, a second grounded drift tube 318, a first powered drifttube 314, disposed downstream of the first grounded drift tube 312, anda second powered drift tube 316, disposed downstream of the firstpowered drift tube 314. In this embodiment, a quadrupole configuration308 is formed integrally with the drift tube assembly 304, where thequadrupole configuration 308 is formed from shaping portions of thevarious drift tubes of the drift tube assembly 304. The drift tubeassembly 304 may be arranged to operate similarly to the drift tubeassembly 204, except that the shape of the quadrupole 308A, quadrupole308B, and quadrupole 308C are defined by elliptical surfaces.

FIG. 4 presents an apparatus showing a drift tube assembly 404 that maybe used as in the drift tube assembly 104, drift tube assembly 204, anddrift tube assembly 304, to accelerate and shape an ion beam, generallyas discussed with respect to FIG. 1 and FIG. 2. A difference in thisembodiment and previous embodiments is that the drift tube assembly 404defines a double gap configuration, shown as gap 1 and gap 2. The drifttube assembly 404 is formed of a plurality of drift tubes, including afirst grounded drift tube 412, a second grounded drift tube 416, and apowered drift tube 414, disposed downstream between the first groundeddrift tube 312 and the second grounded drift tube 416. This drift tubeassembly 404 may be coupled to receive an RF voltage from a single endof a resonator as in known LINAC double gap configurations.Advantageously, a quadrupole arrangement 408 is formed integrally withinthe various drift tubes and is defined by a first quadrupole 408A andsecond quadrupole 408B, defined by sinusoidal shapes as in theembodiment of FIG. 2, to provide better X- and Y-focusing of an ionbeam.

FIG. 5 shows details of the geometry of drift tube apparatus, with aquadrupole arrangement formed integrally therein, according toembodiments of the disclosure. In particular, a section through the Z-Xplane and a section through the Z-Y plane are shown. The drift tubeapparatus is shown as a drift tube assembly 500, including fourelectrodes as generally described above, namely, a first grounded drifttube 502, first powered drift tube 504, second powered drift tube 506,and second grounded drift tube 508. The electrodes (drift tubes) aremodeled as cylindrical shells of thickness of 2*a, which value is 20 mmin the non-limiting embodiment of FIG. 5. In each section, the crosssectional view of a cylindrical shell shows two identical sets ofstructures. FIG. 5 also provides exemplary equations for defining thesurfaces of the electrodes for elliptical or sinusoidal embodiments. Inparticular, in this non-limiting embodiment, to ensure a smoothtransition, the parameter “a” may represent the value for one semi-axisof an ellipse, as well as half the thickness (2a) of the cylindricalshell of the drift tube electrode. The parameter “a” alternativelyrepresents the value of a quarter wavelength in the embodiment of asinusoidal surface. In the case of an elliptical surface, the value of“b” is independent of the radius “r” and may be varied to generatesmall/medium/large protrusions that define quadrupole structures. Thephysical limit of “b” is the gap length for a given gap in a drift tubeassembly.

FIG. 6A and FIG. 6B depict the geometry of ion beam focusing inaccordance with embodiments of the disclosure. In particular, FIG. 6Aand FIG. 6B are plots for the beam envelope of an ion beam in the X-Zplane and the Y-Z plane, respectively, developed from a simulation studywhere P++ions are tracked under an example of defocusing-focusing-defocusing (DOFODO) configuration drift tube configuration 600with quadrupoles (see FIG. 5). The plots illustrate that, under no spacecharge force, a circular beam can be focused on both of two transversedirections by carefully choosing an RF phase (plot for no protrusion).With inclusion of a protrusion, one can clearly observe that for thex-direction the beam undergoes focusing, then defocusing, and thenfocusing (FODOFO), while for the y-direction the beam undergoesdefocusing, then focusing, and then defocusing (DOFODO). At the end ofthe triplet, overall and balanced focusing effect is achieved toward theexit (see lower curves at Z=200 mm).

In other embodiments of the disclosure, a drift tube assembly may bearranged with quadrupoles, wherein at least one gap may be adjustable.Because the quadrupole strength will depend on the length of the gap,and the length and the size of the protrusions forming the quadrupole,the ability to adjust gap length allows quadrupole strength to beadjusted without having to remove or reconfigure parts of a drift tubeassembly.

FIG. 7A shows another exemplary apparatus, according to furtherembodiments of the disclosure. In the apparatus 700, a resonator 102 andRF power generator 120, previously discussed, are shown, and will not bedescribed further. In this apparatus, a drift tube assembly 704 definesa triple gap configuration, shown as g1, g2, and g3.

The apparatus 700 includes a cross structure 730, and support structure722, arm 728, arm 726, and support structure 724, all being mechanicallycoupled to the cross structure 730.. The support structure 722 includesa first arm 722A and a second arm 722B. The first arm 722A ismechanically coupled to a first ground drift tube 712, while the secondarm 722B is mechanically coupled to a first part 714-A of a firstpowered drift tube couple 714.

The support structure 724C includes a first arm 724A and a second arm724B. The first arm 724A is mechanically coupled to a second part 716-Bof a second powered drift tube couple 716, while the second arm 724B ismechanically coupled to a second ground drift tube 718.

The fixed arm 728 is connected to the second part 714-B of the firstpowered drift tube couple 714. The fixed arm 726 is connected to thefirst part 716-A of the second powered drift tube couple 716.

A quadrupole triplet 708 is formed, including quadrupole 708A,quadrupole 708B, and quadrupole 708C, formed in the gaps gl, g2, and g3,respectively. In accordance with some embodiments of the disclosure, arm728, arm 726, first arm 722A, second arm 722B, first arm 724A and secondarm 724B may be independently movable along the Z- axis with respect toone another, which movement enables the change of g1, g2, and g3independently. This adjustment of the size of gl, g2, and g3 may beaccomplished by any suitable means for moving the aforementioned arms,such as external mechanical components, motors, or other components (notshown), while not requiring breaking of vacuum in the beamline orreplacement of drift tube components.

By providing an arrangement where the size of gaps g1, g2, and g3 may bereadily varied, the embodiment of FIG. 7A provides a novel approach tocontrolling beam geometry. While the size of the protuberance for thequadrupoles may be fixed, as defined by the hardware that forms a givendrift tube/quadrupole assembly (such as drift tube assembly 704), thepresent inventors have discovered that the focusing strength provided bya given protuberance may be adjusted by changing the size of gl, g2, andg3. In other words, the size (along the Z-direction) of one or more ofthe gaps may be independently adjusted to adjust the focusing strengthfor an ion beam.

FIG. 7B and FIG. 7C shows an example where the effect of changing thesize of one accelerating gap is shown, such as changing g3. Thesimulation shown illustrates that, by changing Lq3, the focusingstrength generated by a drift tube/quadrupole assembly changes,resulting in a change in beam size. In particular, FIGS. 7B and FIG. 7Care plots for the beam envelope of an ion beam in the X-Z plane and theY-Z plane, respectively, developed from a simulation study where asimple drift tube assembly 750 is schematically represented by fourdifferent blocks, where the rightmost two blocks define a gaps g3. Inthe simulation shown, the relative size of the gap g3 is adjusted whilethe other gap dimensions remain fixed. For the particular ion beamconditions shown, reducing the size of g3 results in decreasing beamwidth in X (at 200 mm), while increasing the beam width in Y. For otherion beam conditions, different mass-to-charge ratio might lead todifferent transit time and other higher order effects, the subsequentbeam focusing behavior may differ from those results shown in FIG. 6Aand FIG. 6B. Notably, the above results illustrate the ability to varybeam focus by adjusting the size of just one gap, while in additionalembodiments, the ability to independently vary the size more than onegap will provide additional beam focusing control.

FIG. 8 depicts a schematic of an ion implanter, according to embodimentsof the disclosure. The ion implanter 800 includes acceleration stages814-A, 814-B of a LINAC, shown as linear accelerator 814. The ionimplanter 800, may represent a beamline ion implanter, with someelements not shown for clarity of explanation. The ion implanter 800 mayinclude an ion source 802, and a gas box 807 as known in the art. Theion source 802 may include an extraction system including extractioncomponents and filters (not shown) to generate an ion beam 806 at afirst energy. Examples of suitable ion energy for the first ion energyrange from 5 keV to 100 keV, while the embodiments are not limited inthis context. To form a high energy ion beam, the ion implanter 800includes various additional components for accelerating the ion beam806.

The ion implanter 800 may include an analyzer 810, functioning toanalyze the ion beam 806 as in known apparatus, by changing thetrajectory of the ion beam 806, as shown. The ion implanter 800 may alsoinclude a buncher 812, and a linear accelerator 814 (shown in the dashedline), disposed downstream of the buncher 812, where the linearaccelerator 814 is arranged to accelerate the ion beam 806 to form ahigh energy ion beam 815, greater than the ion energy of the ion beam806, before entering the linear accelerator 814. The buncher 812 mayreceive the ion beam 806 as a continuous ion beam and output the ionbeam 806 as a bunched ion beam to the linear accelerator 814. The linearaccelerator 814 may include a plurality of acceleration stages (814-A,814-B, ... to 814-Z (not shown)), arranged in series, as shown. Invarious embodiments, the ion energy of the high energy ion beam 815 mayrepresent the final ion energy for the ion beam 806, or approximatelythe final ion energy. In various embodiments, the ion implanter 800 mayinclude additional components, such as filter magnet 816, a scanner 818,collimator 820, where the general functions of the scanner 818 andcollimator 820 are well known and will not be described herein infurther detail. As such, a high energy ion beam, represented by the highenergy ion beam 815, may be delivered to an end station 822 forprocessing a substrate 824. Non-limiting energy ranges for the highenergy ion beam 815 include 500 keV- 10 MeV, where the ion energy of theion beam 806 is increased in steps through the various accelerationstages of the linear accelerator 814. In accordance with variousembodiments of the disclosure, one or more of the acceleration stages ofthe linear accelerator 814 may include a drift tube assembly, withintegrated quadrupole arrangement, as detailed with respect to theembodiments of FIGS. 1-7. An advantage provided by the ion implanter 800is that the focusing of the ion beam 815 as conducted through the linearaccelerator 814 may be improved, due to the operation of the integratedquadrupole configurations.

In view of the above, the present disclosure provides at least thefollowing advantages. As a first advantage, the integration of aquadrupole triplet into a drift tube assembly provides the ability toindependently control focus of ion beam bunches. A second advantage isthat the provision of variable length drift tube assembly of the presentembodiments provides the flexibility to independently control quadrupolestrength.

While certain embodiments of the disclosure have been described herein,the disclosure is not limited thereto, as the disclosure is as broad inscope as the art will allow and the specification may be read likewise.Therefore, the above description are not to be construed as limiting.Those skilled in the art will envision other modifications within thescope and spirit of the claims appended hereto.

1. An apparatus, comprising: a drift tube assembly, the drift tubeassembly comprising a plurality of drift tubes that define a triple gapconfiguration, and are arranged to accelerate and transmit an ion beamalong a beam path; a resonator, to output an RF signal to the drift tubeassembly; and an RF quadrupole triplet, connected to the drift tubeassembly, and arranged circumferentially around the beam path.
 2. Theapparatus of claim 1, the drift tube assembly comprising a plurality ofdrift tubes, wherein the RF quadrupole triplet is integrally formedwithin the plurality of drift tubes.
 3. The apparatus of claim 1, the RFquadrupole triplet comprising: a first quadrupole formed on a downstreamportion of a first grounded drift tube and an upstream portion of afirst powered drift tube; a second quadrupole formed on a downstreamportion of the first powered drift tube and an upstream portion of asecond powered drift tube; and a third quadrupole formed on a downstreamportion of the second powered drift tube and an upstream portion of asecond grounded drift tube.
 4. The apparatus of claim 3, wherein adownstream surface of the first grounded drift tube forms acomplementary match to an upstream surface of the first powered drifttube, wherein a downstream surface of the first powered drift tube formsa complementary match to an upstream surface of the second powered drifttube, and wherein a downstream surface of the second powered drift tubeforms a complementary match to an upstream surface of the secondgrounded drift tube.
 5. The apparatus of claim 4, wherein the firstquadrupole, the second quadrupole, and the third quadrupole define anelliptical shape.
 6. The apparatus of claim 4, wherein the firstquadrupole, the second quadrupole, and the third quadrupole define asinusoidal shape.
 7. The apparatus of claim 3, wherein the drift tubeassembly comprises a first powered drift tube couple, and a secondpowered drift tube couple, wherein the triple gap configurationcomprises a first gap, between the first grounded drift tube and firstpowered drift tube couple, a second gap, between first powered drifttube couple and the second powered drift tube couple, and a third gap,between the second powered drift tube couple and the second groundeddrift tube, wherein a first length of the first powered drift tube isadjustable, and a second length of the second powered drift tube isadjustable.
 8. The apparatus of claim 7, wherein a first part of thefirst powered drift tube couple and the first grounded drift tube aremovable in concert with one another, wherein a second part of the secondpowered drift tube couple and the second grounded drift tube are movablein concert with one another, wherein the first gap, second gap, andthird gap do not vary when a length of the first powered drift tube or alength of the second powered drift tube is varied.
 9. An ion implanter,comprising: an ion source, to generate a continuous ion beam; a buncher,disposed downstream of the ion source, and arranged to transform thecontinuous ion beam into a bunched ion beam; and a linear accelerator,downstream of the buncher and comprising a plurality of accelerationsstages, wherein a given stage of the plurality of acceleration stagescomprises: a drift tube assembly, the drift tube assembly comprising aplurality of drift tubes, defining a triple gap configuration, andarranged to accelerate the bunched ion beam along a beam path; aresonator, to output an RF signal to the drift tube assembly; and an RFquadrupole triplet, connected to the drift tube assembly, and arrangedcircumferentially around the beam path.
 10. The ion implanter of claim9, the RF quadrupole triplet being integrally formed within theplurality of drift tubes.
 11. The ion implanter of claim 9, the RFquadrupole triplet comprising: a first quadrupole formed on a downstreamportion of a first grounded drift tube and an upstream portion of afirst powered drift tube; a second quadrupole formed on a downstreamportion of the first powered drift tube and an upstream portion of asecond powered drift tube; and a third quadrupole formed on a downstreamportion of the second powered drift tube and an upstream portion of asecond grounded drift tube.
 12. The ion implanter of claim 11, wherein adownstream surface of the first grounded drift tube forms acomplementary match to an upstream surface of the first powered drifttube drift tube, wherein a downstream surface of the first powered drifttube forms a complementary match to an upstream surface of the secondpowered drift tube, and wherein a downstream surface of the secondpowered drift tube forms a complementary match to an upstream surface ofthe second grounded drift tube.
 13. The ion implanter of claim 12,wherein the first quadrupole, the second quadrupole, and the thirdquadrupole define an elliptical shape.
 14. The ion implanter of claim12, wherein the first quadrupole, the second quadrupole, and the thirdquadrupole define a sinusoidal shape.
 15. The ion implanter of claim 11,wherein the drift tube assembly comprises a first powered drift tubecouple, and a second powered drift tube couple, wherein the triple gapconfiguration comprises a first gap, between the first grounded drifttube and first powered drift tube couple, a second gap, between firstpowered drift tube couple and the second powered drift tube couple, anda third gap, between the second powered drift tube couple and the secondgrounded drift tube, wherein a first length of the first powered drifttube is adjustable, and a second length of the second powered drift tubeis adjustable.
 16. The ion implanter of claim 15, wherein a first partof the first powered drift tube couple and the first grounded drift tubeare movable in concert with one another, wherein a second part of thesecond powered drift tube couple and the second grounded drift tube aremovable in concert with one another, wherein the first gap, second gap,and third gap do not vary when a length of the first powered drift tubeor a length of the second powered drift tube is varied.
 17. Anapparatus, comprising: a drift tube assembly, the drift tube assemblycomprising a plurality of drift tubes arranged to accelerate andtransmit an ion beam along a beam path; a resonator, to output an RFsignal to the drift tube assembly; and a quadrupole arrangement,arranged circumferentially around the beam path, wherein the quadrupolearrangement is integrated into a surface of the plurality of drift tubesof the drift tube assembly, and wherein the quadrupole arrangementdefines a sinusoidal shape or an elliptical shape.
 18. The apparatus ofclaim 17, wherein the drift tube assembly defines a triple gapconfiguration, and wherein the quadrupole arrangement defines an RFquadrupole triplet.
 19. The apparatus of claim 17, wherein the drifttube assembly defines a double gap configuration.
 20. The apparatus ofclaim 18, wherein the drift tube assembly comprises a first powereddrift tube couple, and a second powered drift tube couple, wherein thetriple gap configuration comprises a first gap, between the firstgrounded drift tube and first powered drift tube couple, a second gap,between first powered drift tube couple and the second powered drifttube couple, and a third gap, between the second powered drift tubecouple and the second grounded drift tube, wherein a first length of thefirst powered drift tube is adjustable, and a second length of thesecond powered drift tube is adjustable.